1

LTC1627

Monolithic Synchronous

Step-Down Switching Regulator

Figure 1b. Efficiency vs Output Load Current

Figure 1a. High Efficiency Step-Down Converter

FEATURES

The LTC

buck regulator using a fixed frequency architecture. The

operating supply range is from 8.5V down to 2.65V, making

it suitable for one or two lithium-ion battery-powered appli-

cations. Burst Mode operation provides high efficiency at

low load currents. 100% duty cycle provides low dropout

operation, which extends operating time in battery-operated

systems.

The operating frequency is internally set at 350kHz, allowing

theuseofsmallsurfacemountinductors.Forswitchingnoise

sensitive applications it can be externally synchronized up to

525kHz. The SYNC/FCB control pin guarantees regulation of

secondary windings regardless of load on the main output by

forcing continuous operation. Burst Mode operation is inhib-

ited during synchronization or when the SYNC/FCB pin is

pulled low to reduce noise and RF interference. Soft-start is

provided by an external capacitor.

Optional bootstrapping enhances the internal switch drive for

single lithium-ion cell applications. The internal synchronous

switch increases efficiency and eliminates the need for an

external Schottky diode, saving components and board

space. The LTC1627 comes in an 8-lead SO package.

L1 15

µH

100

µF

6.3V

80.6k

249k

47pF

2.8V*

TO 8.5V

3.3V

1627 F01a

0.1

µF

22

µF

16V

1

2

3

4

8

7

6

5

SYNC/FCB

SW

RUN/SS

GND

LTC1627

+

+

OUTPUT CURRENT (mA)

1

70

90

95

100

10

100

1000

1627 F01b

85

80

75

s

High Efficiency: Up to 96%

s

Constant Frequency 350kHz Operation

s

s

s

No Schottky Diode Required

s

Synchronizable Up to 525kHz

s

Selectable Burst Mode

s

Low Dropout Operation: 100% Duty Cycle

s

Precision 2.5V Undervoltage Lockout

s

Secondary Winding Regulation

s

Current Mode Operation for Excellent Line and

Load Transient Response

s

Low Quiescent Current: 200

µA

s

Shutdown Mode Draws Only 15

µA Supply Current

s

±1.5% Reference Accuracy

s

Available in 8-Lead SO Package

s

Cellular Telephones

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Portable Instruments

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Wireless Modems

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RF Communications

s

Distributed Power Systems

s

Scanners

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Single and Dual Cell Lithium

, LTC and LT are registered trademarks of Linear Technology Corporation.

Burst Mode is a trademark of Linear Technology Corporation.